This invention relates to manually-directed lasers that emit beams that are not readily visible to the naked eye, such as lasers used for medical applications (e.g., laser tissue soldering), and lasers used in industrial, commercial or research applications.
Manually-directed lasers are used in medical and in industrial applications to direct energy at a target. When the lasers operate at wavelengths which are not readily visible, e.g., near-infrared, infrared, or ultraviolet wavelengths, or when a laser beam which emits visible radiation is pulsed so that it might not be emitting when the operator is aiming the laser beam, it is difficult for an operator to direct the beam at the proper location on the target. One method for resolving this problem is to use a visible beam that is collinear with the non-visible beam. However, that method is often not satisfactory because it does not identify the complete area that is covered by the laser beam, and because it requires a mixing of the optical sources, such that the visible beam and the nonvisible beam are traveling along the same optical path. Furthermore, that method provides no guidance as to whether the correct energy density has been delivered to the target.
A primary medical application that requires delivering energy via laser beams is laser tissue soldering (LTS), as described by Kirsch in Contemporary Urology (Oct. 97, pp. 41-60), which is incorporated by reference herein. LTS is a wound healing technique which bonds the edges of the wound using a protein-based solder activated by energy from a laser. The solder is typically (but not necessarily) mixed with a photon-absorbing dye (or chromophore). The laser used emits electromagnetic radiation at a wavelength absorbed by the photon-absorbing dye and/or the protein-based solder. Solders based on human albumin provide the best strength and leak point pressure upon repair, but various other proteins, including egg albumin, fibrinogen and fibrin have been used. Hyaluronate has been added to solders to increase its viscosity, and may also help cell migration during healing.
Laser tissue welding is a technique which is similar to laser tissue soldering, excpet that it does not use a solder. In that application, the heat is applied directly to tissue with a laser beam.
Many laser-chromophore combinations have been tried. Most studies used the combination of indocyanine green dye (ICG) and a 810 nm diode laser. Laser tissue surgery has been tested successfully in many types of surgery, and is particularly suited for procedures performed on the urinary tract. The advantages of LTS include minimal tissue handling, maximal tissue alignment, maintenance of luminal continuity, water-tight closure, early re-ephithelialization, maximal tensile strength during early healing, no foreign body reaction, and minimal scar formation.
Initially, the typical laser used for LTS (as well as for the related technique, laser tissue welding, which does not use solder) was a relatively large, high-power laser, such as a Nd:YAG laser or a CO2 laser mounted on a bench top. The laser beam was transmitted through a fiber optic cable or through an articulated arm to a hand-held tool. The hand-held tool would be used by the surgeon to direct the laser beam at the tissue to be treated. However, infrared and near-infrared lasers such as the CO2 and Nd:YAG lasers (as well as the 810 nm diode laser mentioned above) are not visible to the naked eye.
More compact laser devices for surgery have been recently developed, e.g., as disclosed in U.S. Pat. No. 5,074,861 issued to Schneider et al. (xe2x80x9cSchneiderxe2x80x9d), U.S. Pat. No. 5,272,716 issued to Soltz et al. (xe2x80x9cStoltzxe2x80x9d), and U.S. Pat. No. 5,553,629 issued to Keipert et al. (xe2x80x9cKeipertxe2x80x9d), which are all incorporated by reference herein. Schneider discloses an erbium YAG laser that transmits the laser energy from the laser to the tip of the probe using a light horn or mirrors. Soltz discloses a semiconductor laser diode system which utilizes two lasers: one laser is a guide laser, providing visible radiation, and one laser supplies the energy to the xe2x80x9cworkpiece.xe2x80x9d The two lasers are focused and collimated by a pair of lenses so that they travel identical paths. Keipert et al. disclose a laser apparatus which includes infra-red viewing goggles, so that the surgeon (or other operator of the device) could see the infrared beam.
U.S. Pat. No. 5,147,349 issued to Johnson et al. discloses an infrared diode laser for use in transcutaneous laser photocoagulation of the retina. This laser is optimized for use in the retinal surgery. The specification also discloses the use of a visible laser beam, such as a He-Ne laser, which is optically merged with the infrared diode laser beam, so that the merged beam is visible. However, this system does not define the incident area of the nonvisible beam, or provide any method for determining whether the correct power density and energy density is being delivered to the target.
Accordingly, it is an object of the present invention to provide the correct energy density (for pulsed systems) and power density (for continuous systems) to a well defined target area when using a laser system with a nonvisible laser beam.
It is a further object of the present invention to provide a hand-held self-contained laser system which has been optimized for use in medical procedures such as laser tissue soldering or laser tissue welding, as well as in industrial, commercial or research applications.
It is also an object of the present invention to provide a method of use of a laser system with a nonvisible beam for laser tissue soldering and for laser tissue welding.
xe2x80x9cManually directedxe2x80x9d as used herein with reference to directing a laser beam means that the laser beam is directed by a human operator, whether that operator holds a hand-held laser in his hand, holds an aiming tool connected to a laser by an optical fiber, or uses mechanical, electric, electronic, automated or computerized controls to physically direct the laser beam.
A xe2x80x9cnonvisible beamxe2x80x9d is a beam that is not visible to the operator of the laser system at the time the operator needs to direct the laser for a variety of reasons, including (1) the beam is a near-infrared, infrared or ultraviolet beam that is not readily visible to the naked eye; (2) the beam is pulsed; (3) the laser must be precisely directed before it is turned on; (4) the operator is wearing safety goggles which block the wavelength of the laser beam.
The xe2x80x9coptimum distancexe2x80x9d is the distance from the output of the collimating lens at which the power density of the nonvisible beam is at a broad maximum.
The present invention is a laser system that provides a collimated nonvisible laser beam output, and one or more (laser or non-laser) visible beams that define the location and periphery of the nonvisible beam, and that provide feedback to a human operator such that the operator can maintain the optimum energy/power density at the target. The system comprises at least one nonvisible laser source optically coupled to an optical fiber, at least one visible (laser or non-laser) source optically coupled to one or more optical fibers that deliver visible beams that define the location and periphery of the nonvisible beam at the target, and collimating optics for collimating both the nonvisible laser beam and the visible beams. The collimating optics focus the visible beam such that, when the visible beam is in focus at the target, the nonvisible beam has the optimum energy/power density at the target.
FIG. 1a illustrates the divergence of a beam from an uncollimated fiber 1. FIG. 1b shows the beam profile when collimating optics 2 are placed in front of fiber 1. At about position 4, which is at a distance bb from the output of the collimator, the spot size of the beam is relatively constant over a certain range, i.e., the power density of the beam will not vary greatly over that range on either side of position 4. This characteristic is illustrated by the collimated beam example shown in the line plot with the solid circles in FIG. 2a, where position 4 in FIG. 1 corresponds to the center of the broad maximum at a distance of 14 cm on the abscissa of FIG. 2a. Over a range of 4 cm on either side of 14 cm, i.e. from 10 cm to 18 cm, the power density of the beam is 15xc2x12 watts/cm2, a variation of about xc2x114% over the 8 cm. The line plot without solid circles in FIG. 2a is a representation of the power variation as a function of distance for an uncollimated beam (the units on the y-axis apply only to the collimated beam plot, and do not apply to this line plot). As FIG. 2a shows, the uncollimated beam is reduced by roughly a factor of three over 8 cm. FIG. 2b is another example of a collimated beam output. This Figure shows that the power density is roughly constant, for this example, over a 5 cm range. FIG. 2c is an example of the laser power density for an uncollimated beam. This plot shows a very steep decline in the power density, and a relatively short working range for the device. For example, if the power density needs to be at 5 watts/cm, FIG. 2c shows that laser system should be positioned at a distance of 1.1 cm from the target area. A change of only 1 mm on either side results in a change of roughly 20% in power density.
Preferably, the power (or energy, for pulsed systems) density should vary by no more than 10% per cm over a range of 2 cm on either side of the optimum distance. Also, the visible light beam should be in sharp focus at approximately the optimum distance, i.e., within 5 mm from the optimum distance.
FIG. 3 is a schematic diagram of the basic components of the present invention. As shown in FIG. 3, the beams from nonvisible laser 9 and visible light source 10 are optically connected using optical fibers 5 and 6, respectively. Visible light source 10 is, e.g., a light emitting diode emitting green light. Visible light source 10 could also emit orange or yellow light, or any other color or mix of colors (including white light) which provides good contrast on the target, and which is readily seen through the protective goggles the operator may be wearing. Optical fiber connector 7 is used to position the optical fiber(s) from the nonvisible laser(s) at the center of the bundle of optical fibers, i.e., the optical fiber carrying the nonvisible beam is surrounded by two or more optical fibers carrying the visible light beams. Collimating lens 8 collimates the light output from optical fibers 5 and 6.
For most applications the present invention uses one nonvisible laser 9 and one optical fiber 5 for the nonvisible Laser beam. Optical fiber 5 is surrounded by two, three, four or more optical fibers from the visible light source (s), as shown in FIGS. 4a, 4b, 4c, 4d, 4e, 4f, and 4h although use of multiple nonvisible optical fibers is also possible, as shown in FIG. 4g. The present invention is preferably implemented with at least six optical fibers (FIG. 4d) and more preferably with at least eight optical fibers (FIG. 4e). Collimating optics 8 are used to collimate the nonvisible beam and the visible light beams, such that both the visible beams and the nonvisible beam are in focus on the target when the laser output is positioned at the optimal distance from the target. This effect is illustrated in FIG. 4i, which shows the appearance of the spots on the target from the visible light beams in sharp focus when the laser output is at the optimal distance from the target (the middle drawing) compared to when the laser output is too close (the left drawing) or too far away (the right drawing)Dark lines 17 on FIG. 4i outline the size of the nonvisible beam at the target as a function of the distance of the laser output from the target. At the optimal distance the size 15 (preferably 1.5 mm to 10 mm in diameter) of the nonvisible beam is at a very broad and shallow minimum (corresponding to a broad maximum in energy density), as shown in the middle drawing of FIG. 4i. 
FIGS. 4j and 4k illustrate a second preferred embodiment of the present invention. As shown in FIG. 4j, the optical fiber used to transmit the nonvisible laser beam for the embodiments of the invention shown in FIGS. 4a-4i consists of a central core 20 and an outer cladding 21. In the second preferred embodiment, shown in FIG. 4k, the optical fiber consists of an inner cladding 22 in addition to the central core 20 and the outer cladding 21. In this embodiment, the nonvisible laser beam is transmitted through central core 20 and the visible light beam is transmitted through inner cladding 22. The output of the fiber shown in FIG. 4kis thus a nonvisible laser beam within a ring of visible light.
An example of a specific hand-held implementation of a preferred embodiment of the present invention is described below as Example 1. This implementation is particularly well-suited for laser tissue soldering. In Example 1, the laser is incorporated in a battery-powered self-contained hand-held apparatus with a roughly uniform distribution of light intensity across the beam. The laser apparatus provides laser energy at a wavelength absorbed by the chromophore utilized in the laser solder with optimum parameters for tissue soldering.